1. Field of the Invention
The present invention relates to a method and an apparatus for feeding a sheet, used with recording systems, and more particularly, it relates to a sheet feeding method and apparatus adapted to feed a transparent plastic sheet.
2. Related Background Art
In the past, a transparent plastic sheet has been exclusively used as a sheet for an OHP (overhead projector) (referred to as "OHP sheet" hereinafter), which included a recording or printing surface constituted by, for example, a coating layer coated on a polyester sheet.
The OHP sheet has been used for recording or displaying thereon images or characters by means of an overhead projector (OHP).
As to the OHP sheet, a sheet having coating layers on both of its surfaces has generally been used, for the reason that, if such coating layer is provided on only one of the surfaces thereof, the sheet will be in danger of curling due to heat and/or moisture generated in the recording operation.
However, in the conventional recording system, there arose a problem that when the images were printed on the OHP sheet having the coating layers on both surfaces thereof the coating material adhered to a heater of a fixing device to smear the heater and/or the next OHP sheet.
Further, in general, the OHP sheet is sold in the market as a stack or laminated package in which the OHP sheets and plain sheets (as separating sheets) are stacked or laminated alternately. If such stacked sheets are used as they are in the conventional recording system, the OHP sheet and the plain sheets are alternately fed one by one in a recording station of the recording system. Accordingly, in this case, there arises a problem that not only the plain sheets (separating sheets) must be prevented from being fed in the recording station, but also the coating material on both surfaces of each OHP sheet adheres to the heater of the fixing device to smear the heater and/or the next OHP sheet as mentioned above.
In order to solve this problem, a method for feeding OHP sheets properly by preventing adhesion of the OHP sheet to a paper holder plate in a high temperature and high moisture condition has been proposed, as described in the Japanese Patent Laid-Open No. 61-173971 (corresponding to U.S. Ser. No. 820,747 filed on Jan. 22, 1986 now abandoned). According to the proposed method, a plurality of ridges or projections were formed on a surface of the paper holder plate on which the OHP sheet was guided, thereby reducing friction between the OHP sheet and the paper holder plate to prevent oblique movement and/or uneven feeding of the OHP sheet even in the high temperature and high moisture condition.
However, even if the method described in the above Japanese Patent Laid-Open No. 61-173971 was used, the drawback that the coating material of the OHP sheet having the coating layers on both of its surfaces adhered to the heater of the fixing device to smear the heater and/or the next OHP sheet could not be eliminated completely.